Change logo src to https to avoid mixed-content

    The page at 'https://github.com/oreoshake/Haxl' was loaded over HTTPS, but displayed insecure content from 'http://github.com/facebook/Haxl/raw/master/logo.png': this content should also be loaded over HTTPS.

    curl https://raw.githubusercontent.com/facebook/Haxl/master/logo.png 200OK